Suction box cover



Sept. 15, 1964 J. J- STEVENSON SUCTION BOX COVER Filed Jan. 2, 1963 Q Q Q Q Q 0 0 0 0 C) 0 0 0 0 0 0 0 0 0 0 0 o 0 United States Patent 3,149,629 SUCTION BOX COVER James I. Stevenson, Erie, Pa., assignor to Continental Rubber Works, Erie, Pa., a corporation of Pennsylvania Filed Ian. 2, 1963, Ser. No. 248,939 9 4 Saints. (Cl. 162-374) In paper making machines, the pulp is discharged onto wires which run over suction boxes having perforated covers through which water is sucked out of the pulp. The early suction box covers were made of wood and many suction box covers still are made of wood. More recently, in an effort to get a smoother surface, stainless steel, plastic and silicon carbide covers have been suggested. These more recent covers proceed on the theory that the suction box covers should have a smooth surface in order to reduce friction between the suction box covers and the wires.

This invention is a suction box cover which proceeds on the theory that the surface of the cover should not be smooth, but, on the contrary, should have numerous fine pits which trap air and water and cushion the wires so that the wires never really come in contact with the suction box covers and, accordingly, are not abraded away. This is an important advantage. In the past, paper making machines have been shut down every two or three weeks to replace the worn wires. With the present invention, the operating period between shut-downs can be extended by a factor of two or three.

In the drawing, FIG. 1 is a fragmentary view of a suction box cover and FIG. 2 is a magnified view of the pitted surface over which the wire runs.

The suction box cover 1 is shown in one of the conventional designs having round perforations 2. These perforations are not critical. Non circular, elongated, zig-zag, slotted, and other forms of perforations may be used. The suction box cover is mounted on top of the suction box in the same manner as the wood, metal, plastic, or other suction box cover it replaces. After mounting, the upper surface of the cover over which the wires run is ground flat to prevent loss of suction.

The material of the cover is hard rubber (e.g. Pusey and Jones plastometer reading of 1 with /s" ball) having uniformly dispersed therein fine rock particles which are unbonded to the rubber. When the upper surface of the suction box cover is finish ground, the great majority of the rock particles at or adjacent the ground surface fall out or are knocked out of the rubber, leaving the finish ground surface peppered with small pits. These pits appear only where the particles have been exposed by the grinding operation. Beneath the pits the particles are still embedded in the rubber and provide a solid, strong, subsurface which is dimensionally stable. The finish ground surface when viewed directly appears to be highly polished, but when viewed sideways appears to have numerous fine pits.

In the suction box cover there is a continual flow of air and water through the perforations and the wires of the paper machine are passing at high speeds over the finish ground surface of the cover. The pits in the surface trap air, providing a cushion for the wires which greatly reduces the friction load and wear on the wires. Paper machines shut down at the regular two to three week intervals show negligible wear on the wires. Since the wires are the critical element requiring shut down of a paper machine, this means that the period between "Ice shut-downs can be extended by a factor of from two to five times, depending upon the life of other parts of the paper machine. It will be understood that when a machine is shut down, many parts which are only slightly Worn are replaced because of expected wear during the succeeding operational period. Paper machines run 24 hours a day, 7 days a week and, barring operational failure, are shut down only for the periodic replacement of worn parts.

For the hard rubber, butadiene copolymer elastomers are preferred because of their oil resisting properties and because the butadiene elastomers do not bond to the rock particles. Natural hard rubber bonds to the rock particles unless the particles are specially treated with a releasing agent to prevent bonding. If the rock particles were bonded into the hard rubber, they would not fall out during the finish grinding and would present a rock or abrasive surface which would increase the wear on the wires. Instead of the abrasive surface of rock particles, applicants suction box cover has trapped air bubbles which have no abrasive effect on the wire.

The unbonded rock particles have the additional advantage that as the hard rubber wears, the surface becomes continually renewed as underlying rock particles are exposed and fall out, thereby renewing the pitted surface so that the characteristics of the operative surface are not affected by wear.

The rock material is not critical. It forms a part of the solid subsurface of the suction box cover but it is intended that the rock particles fall out of the active surface to provide the air trapping pits which reduce the friction on the wires. A readily available rock material is natural crystal quartz grade 1/0 having particles which will pass through a 94 mesh screen and will be retained on a 115 mesh screen. This material is used in quantities of from /3 to the weight of the hard rubber, although these proportions are not critical. Fine par ticles are preferred. Particles of relatively uniform size are likewise preferred so that the surface will be essentially uniform.

What is claimed as new is:

1. A perforated suction box cover for a paper machine comprising hard rubber having uniformly dispersed therein fine rock particles unbonded to the rubber and said cover having a finish ground operative surface in which the great majority of the particles exposed by finish grinding have fallen out so that said finish ground surface is a smooth essentially rock free surface peppered with fine pits throughout which trap air and reduce the friction and wear on the wires while the unexposed particles remain in the rubber to provide a hard subsurface supporting and maintaining the flatness of the finish ground surace.

2. A suction box cover as claimed in claim 1 wherein said covering comprises hard butadiene copolymer rubber.

3. A suction box cover as claimed in claim 1 wherein the fine rock particles are silica particles.

4. A suction box cover as claimed in claim 1 wherein said fine rock particles are of substantially mesh.

References Cited in the file of this patent UNITED STATES PATENTS 342,497 Bradbury May 25, 1886 2,280,208 Wilkie Apr. 21, 1942 2,717,540 Planer Sept. 13, 1955 2,989,352 Schmidt June 20, 1961 

1. A PERFORATED SUCTION BOX COVER FOR A PAPER MACHINE COMPRISING HARD RUBBER HAVING UNIFORMLY DISPERSED THEREIN FINE ROCK PARTICLES UNBONDED TO THE RUBBER AND SAID COVER HAVING A FINISH GROUND OPERATIVE SURFACE IN WHICH THE GREAT MAJORITY OF THE PARTICLES EXPOSED BY FINISH GRINDING HAVE FALLEN OUT SO THAT SAID FINISH GROUND SURFACE IS A SMOOTH ESSENTIALLY ROCK FREE SURFACE PEPPERED WITH FINE PITS THROUGHOUT WHICH TRAP AIR AND REDUCE THE FRICTION AND WEAR ON THE WIRES WHILE THE UNEXPOSED PARTICLES REMAIN IN THE RUBBER TO PROVIDE A HARD SUBSURFACE SUPPORTING AND MAINTAINING THE FLATNESS OF THE FINISH GROUND SURFACE. 